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POSIX.2 subclause 5.24 specifies the semantics of the “renice” utility.
During the development of a
conformance test for POSIX.2 questions about this utility have arisen. In
subclause 5.24.2 the utility's
behavior is described as follows:
The renice utility shall request that the system scheduling priorities (see
2,2,2,177) of one or more
running processes be changed.
Further, in subclause 5.24.8 the exit status of renice is specified as
0 Successful completion
>0

An error occurred
Is it conforming for an implementation to return 0, meaning that the
request is noted and is syntactically
correct, but to ignore it or to honor it partially? That is, can a system return 0
but not change the specified
process's priority? Can a system return 0 and change the process's
priority, but not to the extent
requested?
Further, is there any guarantee that the priority schedule change, if
honored, will persist for any period?
For example, can a shell script rely on using a call such as
ps -o nice -p
to determine whether the scheduling priority of process has been
changed in accordance with the
request?

Interpretation Response
Question 1: yes
Question 2: yes
Question 3: yes, the standard clearly states this behaviour on page 594,
lines 3796-3800.
Question 4,
Question 5:
The standard does not speak to this issue, and as such no conformance
distinction can be made between
alternative implementations based on this. This is being referred to the
sponsor.